In a number of manufacturing situations, seal features such as caps and sealant are often placed over fastener ends and nuts, e.g., inside composite fuel tanks in aircraft in order to prevent discharges from lighting strikes from transferring from the fastener into the fuel tank. A lack of a physical bond between the sealant and the interior (as in the composite fuel tank example), or cracks in the seal feature, may reduce the level of protection. Other than visual inspection by human inspectors, there is no known method of inspecting the seal features either during manufacture or in an operational situation (especially in the case of an aircraft) to determine whether the integrity of the seal features has been compromised.